1. Technical Field
The present invention relates to an optical detection device, an electro-optical device, an electronic apparatus, and an optical degradation correction method.
2. Related Art
Generally speaking, the leakage current of a thin film transistor is proportional to the amount of light irradiated thereto. Utilizing such proportionality, an optical detection device of related art detects the amount of irradiating light by accumulating electric charge at a voltage detection capacitor or discharging electric charge that has accumulated thereat by means of the leakage current (optical leakage current) and then by monitoring a voltage change between two terminals of the capacitor. An example of such an optical detection device of related art is described in, for example, JP-A-2006-29832.
The electric characteristics of a thin film transistor degrade optically due to exposure to light. For this reason, the related-art optical detection device described in JP-A-2006-29832 has a disadvantage in that the detection accuracy of the amount of irradiating light lowers as the electric characteristics of a thin film transistor changes due to such optical degradation. In an effort to overcome such a problem, a photoelectric conversion element that has enhanced degradation resistance characteristics, which are obtained by improving the method of forming a thin film transistor, has been proposed. An example of such an improved photoelectric conversion element is described in JP-A-9-232620. As another example of related art that is directed to overcome such a problem, as described in JP-A-2006-179478, a method for correcting a characteristic change due to optical degradation with the use of an analog signal processing circuit that compares the output signal of a photo sensor and a reference signal has been proposed.
However, the photoelectric conversion element described in JP-A-9-232620 has a disadvantage in that it requires special manufacturing conditions, which results in an increase in manufacturing cost. Specifically, when manufacturing photo sensors inside a display device that uses thin film transistors or manufacturing a display device and photo sensors by means of the same manufacturing apparatus, it is not practically possible to manufacture them in the same process as the manufacturing process of the driving transistors of the display device. Accordingly, the photoelectric conversion element described in JP-A-9-232620 requires an additional manufacturing process or the troublesome condition setting of the manufacturing apparatus. The technique described in JP-A-2006-179478 requires an analog signal processing circuit that has a complex circuit structure in order to perform correction processing and a signal source that is used for generating a reference signal, which increases production cost.